In the field of "curable" or cross-linking plastics and rubbers, those which can be cured at room temperature have been of great commercial value. Typically, two or more liquids or pastes are combined in predetermined ratios to bring about a chemical conversion to a solid plastic or rubber. The earliest application of this idea consisted of two fluids which were placed together in a single container and mixed until uniform. The uniform mixture was then placed into appropriate application equipment and then applied. Those procedures were reasonable for low viscosity products which remained fluid for a long period of time. However, with high viscosity fluids, or those which cure very rapidly, batch processing is not practical.
Various mixing arrangements have been devised to overcome those disadvantages. For example, in U.S. Pat. No. 3,144,966 to Cook, a two-chambered dispenser is provided for mixing the fluids together. Another example consists of pumping the material through mechanical mixing devices placed just before the point of application. These devices have generally been too awkward and heavy because a driving mechanism and power source must be supplied to the mixing head. Moreover, when the size was minimized to allow for some mobility, the mixing mechanisms has to operate at higher speeds for more effective mixing. The higher speeds produced local overheating and curing of the materials. Cleaning of the mechanisms has been very difficult and if material cures inside the driving mechanism, an expensive piece of equipment may be lost.
Static mixing devices have been employed to overcome the disadvantages of mechanical mixing. For example, Harder, U.S. Pat. No. 3,404,869 and U.S. Pat. No. 3,583,678 show typical static mixing devices. In prior art devices utilizing static mixers, it was common to mount the static mixer near the source of supply, then extend tubing from the mixer to a dispenser. It was found that a long and bulky static mixing chamber was needed to affect proper mixing. The chamber was mounted on a permanent support and the material flowed through a flexible hose to a hand-held dispenser. However, because the chamber and the flexible hose leading from the chamber was filled with mixed materials, the materials would have to be removed from the respective elements in order that they not cure within the chamber and hose. As the length of the hose increased, the amount of material inside the hose increased so that as a result, each time the device was shut down, a large amount of material would be lost.
With the prior systems, an auxiliary solvent system had to be provided to clean out the mixing chamber and the fluid line. Not only does this add another line into the system, but requires the consumption of large amounts of solvent. The loss of solvent is especially important because most solvents are hydrocarbons derivatives which are becoming more scarce and costly.
An additional problem with such prior art devices is that if the final material is of rapid curing, it must be dispensed out the dispensing end prior to curing. As the curing time decreases, it may be possible that the material will not flow all the way out of the hose and dispensing end prior to curing. This can either result in internal curing which will result in the loss of the equipment, or will limit the length of the hose leading from the mixing chamber. Any limiting of the length of hose is undesirable in that it limits portability to the dispensing end of the device. Even if the hose is short enough so that material will not be cured when it leaves the dispensing end, if the flow is interrupted for even a short period of time, the curing time may be reached within the hose or the chamber and the equipment could be ruined. In certain instances, it became practical to maintain the flow through the system even though the resulting compound had to be wasted because shutting the system down even for a brief time risked expensive equipment.
It is therefore an object of this invention to provide a portable dispensing apparatus for dispensing a composition of at least two materials. This should be done to minimize the potential lost of equipment resulting from curing of material within the system. A further object is to eliminate the secondary solvent system for cleaning materials from within the system. It is desirable to eliminate the waste of solvent and waste of extra components of the mixture. Another object is to improve the mixing of the system while using a smaller static mixer. Still another object of the invention is to provide a device wherein material can be dispensed from a portable, hand-held device which can be directed in any location to localize the application of material and wherein a valve actuator is located on the hand-held device to control the application of materials.